Thank you for sharing, we all agree that this confirmation button or the undo option. I would bring it up to the developers and see where this goes. However, this was suggested before, unfortunately it was not something that was seen to improve the game. Due to the nature of all boosters would be flagged for any use and would make using multiple ones more tedious. Therefore we can suggest it again, but an answer had already been provided previously.
The game will bring you different challenges throughout different events to keep it fresh.
You received troop instant prizes before, in prior events. Therefore, some players who choose not to deplete themselves from these spells will have them available for this quest. Furthermore, @Thezza, we already had one day (5th day) where you could win these spells. We are sorry the negotiate aspect did not work for you, one more reason to never deplete your spells! Keepers always have!